Underwater robots powered by motion through the ocean

The US Navy will be testing two new robotic gliders powered by simply swimming through the sea. The autonomous underwater vehicles will be tested off the coast of California next year, and will perform a range of measurements as they swim through the ocean.

The first of underwater robots developed by laboratories supported by the Office of Naval Research, the Slocum Glider, generates energy from the temperature changes in the ocean. As it moves through the thermocline – a region where the temperature changes rapidly – it cycles thousands of times in a vertical zig-zag between the warmer surface waters and underlying cooler waters, down to a programmed depth of 5,000 feet. The heat flow in the surrounding water generates enough energy to change the robot’s buoyancy.

The underwater robot, named after Captain Joshua Slocum who sailed alone around the world in a 37 foot sloop, is designed to measure salinity and temperature, plot currents and eddies, count microscopic plants and even record biological sounds like whale songs.

The second robot, a Seaglider, is propelled by buoyancy control and wing lift to alternately dive and climb along slanting paths. It uses the Global Positioning System (GPS) to fix its position and navigate through a sequence of programmed points, and can also transmit and receive data via satellite when its antenna is above the sea surface for a few minutes between dive cycles.

The Seaglider has enough range to cross an entire ocean basin in month-long missions, diving to 3,500 feet while it collects high resolution profiles of physical, chemical, and bio-optical properties of the ocean.

The Navy plans to use the robots to check for mines and other countermeasures in foreign waters. The gliders should reduce the need for Marines to enter dangerous shallow waters to clear mines in preparation for other operations.

A UK company recently unveiled a boat engine with a similar propulsion system, using steam power to generate temperature differentials (see related story).

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